Researchers say frequent dental X-rays may increase the risk of the most commonly diagnosed brain tumor in adults in the U.S.

Meningiomas are generally benign, non-cancerous tumors that develop from the membranes that surround the brain and spinal cord. Most such tumors are triggered by exposure to ionizing radiation, such as that from X-rays (and in a small set of cases, from atomic bomb blasts), and many develop after prolonged or high-level exposure. But researchers led by Dr. Elizabeth Claus of the department of epidemiology and public health at Yale University found that low-level exposure to radiation from dental X-rays was also associated with an increased risk of the tumors.

For the study, Claus’s team looked 1,433 patients who were diagnosed with meningiomas in five states between 2006 and 2011, and compared them with 1,350 people without tumors. The researchers compared their self-reported lifetime dental X-ray histories, and found that those with tumors were more than twice as likely to report having had at least one bitewing X-ray of their teeth (in which a technician takes pictures of the upper and lower back teeth to check for cavities or alignment problems).

As disturbing as that sounds, Claus says there are two things people should keep in mind when interpreting these results. First, while most of the people in the study were diagnosed in recent years, their dental X-ray history stretched back a decade, if not more, to a time when ionizing radiation levels were much higher in dental X-rays than they are now. (The mean age of those with the tumors was 57.5 years.) Second, the study compared cases of meningioma to similar controls, rather than asking people about their dental X-ray history and then following them to see who developed meningiomas and who did not.

“We still don’t know what the risk is,” says Claus, who is also on faculty at Brigham and Women’s Hospital in Boston. “We started with the outcome, meningioma, and then looked at exposure. We still need to do a cohort study, but the expense and time [required] may not make that feasible.”

Claus and her team did adjust for potential factors that could influence either the frequency of getting dental X-rays or the incidence of mengiomas, such as whether the participants had had CAT scans of the head or therapeutic radiation to treat other cancers, or even geographic and socioeconomic biases. (The study occurred before many of the current X-ray-based airport scanners were put into place, another potential source of radiation exposure, so the participants were not asked about their air travel history.) Even after accounting for all of these factors, however, the relationship between dental X-rays and meningiomas persisted.

Still, Claus says the results shouldn’t discourage people from seeing their dentist and getting X-rays — if they need them. The important message is that patients should speak with their dentists about whether each X-ray is really essential. Most people may be getting too many dental X-rays and thus exposing themselves to unnecessary risk, says Claus. The American Dental Association currently recommends that healthy adults get dental X-rays once every 18 months to three years, but the participants in the study reported getting more frequent bitewing images. “We saw a big difference between the frequency of people reporting dental X-rays and the frequency suggested in the guidelines — almost double in number of what people are getting versus what is suggested,” says Claus. “That is where we say, Let’s get the information out there, let’s have patients and dentists talk about this and see if for a given patient, we might be able to reduce the number of dental X-rays they get. That’s the more important message.”

So before you open wide at your next dental visit, ask you doctor whether you really need another set of X-rays of your teeth.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

Dental x-ray is being used for every dental treatment whether it is required or not. This article has really exposed the risks involved in x-ray. Study has proven that the frequent dental X-rays, particularly in kids, increase risk of the most common brain tumour.